Trunk-line signaling apparatus and circuit for telephone-exchanges



(No Model.) 2 Sheets--Sheet 1.

R. J. HALL. y TRUNK LANE SIGNALING APPARATUS AND CIRCUIT PoR TELEPHONERXGHANGRS.

(No Model.) 2 Sheets-Sheet',V 2.

E. J. HALL.

TRUNK LINE SIGNALING APPARATUS AND CIRCUIT FOR TELEPHONE EXCHANGES.

No. 491,553. Patented Peb. 14, 1893.

Fig. 2.

NITED STATES PATENT OFFICE.

EDIVARD J. HALL, OF MORRIS, NEW JERSEY, ASSIGNOR TO THE AMERICANTELEPHONE AND TELEGRAII-I COMPANY, OF NEIV YORK.

TRUNK-LINE SIGNALING APPARATUS AND CIRCUIT FOR TELEPHONE-EXCHANGES.

SPECIFICATION forming part of Letters Patent No. 491,553, dated February14, 1893.

Application tiled October 13, 1892. Serial No. 448,763. (No model.)

To all whom it may concern:

Be it known that I, EDWARD J. HALL, residing at Morris township, in thecounty of Morris and State of New Jersey, have invented certainImprovements in TrunleLine Signaling Apparatus and Circuits forTelephone-EX- changes, of which the following is a specilication.

This invention relates to the construction io and operation of telephonecircuits7 and especially of trunk lines extending between centralstations for the purpose of affording facilities whereby telephonesubstation circuits converging to any two central stations respectively,may be interconnected with one another.

The main objects of the present invention are to provide for dividedswitchboard and other central office systems of apparatus, a doubleconductor trunk circuit or line with an etcient and economicalreciprocallyoperating arrangement of signals whereby a connection ordisconnection made therewith by any other circuit or conductor at eitherend thereof shall be caused to automatically announce itself at theother end, and to accomplish this provision without necessitating theconstruction of additional main line conductors for such signal service.

In pursuance of this object the invention consists in combining systemsof divided switchboards, including their necessary connection devicesand office trunk conductors with inter station trunk conductors fitted 35 with a reciprocal signaling system, whereby connections anddisconnections at either end of said trunk may be indicated at theother, without the necessity of constructing special conductors for suchsignaling system.

It also consists in so arranging the two main line conductors of a trunkline, that the said conductors respectively shall also be the main lineconductors of independent signaling circuits terminating at the trunkline stations.

It also consists in providing that the conversation circuit extensionsof such main line conductors shall connect therewith through theintermediation of condensers, tending thereby to form inductivelycomplete double 5o conductor telephone circuits, while the signalextensions of the two main line conductors respectively shall directlyand conductively connect with the ends thereof, and shall eX- tend toearth or to a suitable return conductor, including in their circuit thesignal devices and also electromagnetic resistances or self inductioncoils. Also in so arranging the signaling apparatus of the two circuitswhose independent line sections are respectively the direct and returnconductors of the main cir- 6o cuit that the signal receiving apparatusof one ot them shall be at the same station as the signal transmittingapparatus ofthe other, the transmitting branch of each being normallyopen at the two terminal stations respectively, the two signalingcircuits respectively being thus normally open at opposite ends of thetrunk line, and each being permanently closed at its remaining end. Thusone of the said signaling circuits is closed 7o through its signalingreceiving appliances at Aand normally open at the branch including itstransmitting appliances at B, while the other is closed at B through itssignal receiving appliances, its transmitting end being open at A.

It further consists in providing each signal circuit with a suitablesource of electricity, and with means for its automatic closure by theact of makinga conversation circuit trunk 8o connection at itstransmitting end; and for automatically breaking again the same circuiton the disconnection of said conversation circuit, whereby a suitablesignal is caused to be setat either end of the trunk line, by the act S5of making a connection at the other; the said signal remaining setduring the continuance of such connection; and being caused to disappearwhen the said connection is discontinued.

It also com prises certain details of construction and connection morespecifically set forth in the several clauses of claims, recited at theend of this specification.

In a separate application for Letters Patent 95 filed of even dateherewith, I have described a system of divided switchboards with whichis associated an arrangement of visual signals and circuits the wholebeing entitled an improvement in central office apparatus and roocircuits for telephone exchanges Serial No. 448,762; and in the presentinvention the saine specific form of signaling device and mode ofoperation and many of the same forms of apparatus may be employed oradopted, but I make no claim herein to such appliances, my presentinvention concerning itself solely with trunk line signaling, and withmeans and modes of accomplishing the same by circuits independent of thetelephone circuit, which independent circuits however utilize theconductors of the said telephone circuit.

My present invention may however be regarded as being auxiliary to thatdescribed in said specification, since it is conveniently applicable tothe said system of divided switchboards, and since I contemplate itsoperation in such an association.

In the drawings which form a part of this specification, Figure l is ageneral diagram,`

showing the course of a compound telephone circuit through two centralstations fitted with divided switchboards and united by a trunk line.Fig. 2 is a diagram illustrative of the principles of my invention, andFigs. 3 and 4 are respectively, forms of signal receiving` ap` paratuseither of which is well adapted for use in connection with my invention.

Similar letters and figures of references in the several drawings referto similar features.

In Figs. I and 2, O and O2 are central telephone stations, O and D formthe divided switchboard of O; and C2 and D2 the divided switchboard ofO2.

D and D2 areanswering or terminal switchboards, subdivided intooperators sections,

cachot which is provided as usual with call initial connections anddisconnections aremade, and the substation required on any call, may berung up; and the answering springjackof the substation lines aredistributed Vbetween them.

The connecting boards C and C2 need not be subdivided. On these aremounted springjacks or plugsockets for all of the entering substationlines, and by means of the said jacks, complete connections resultingfrom calls received at the terminal switchboard are effected with anydesired circuit, as more fully specified in my said separate applicationto which reference has been made.

To each central station in practice, a number of substation linesconverge, although to avoidV complication I have shown but two.

L is a circuit leading from a substation A to central station O, and L2a similar circuit leading from a statoin B to the central station O2. Lentering its central station, passes iirst to its jack or socketj on theconnecting board C, and thence to its jack or socket J at some onesection of the terminal board D where also it is provided with a callannunciator a;

vthrough the jacks in question.

and in like manner L2 is led successively through jacks y2 and J2 to itsannunciator a2.

A series of office trunks are provided in this system extending betweeneach section of the terminal board to different points on the connectingboards, and by means of these, the plug receiving connection of acalling circuit on the terminal switchboard may be electrically unitedwith the plug receiving connection of a called circuit at the connectingboard. Again for the sake of an easy understanding, I have shown but onesuch office trunk at its each central station. At station O, the saidtrunk is represented by the letter and at O2 by t2. Preferably the saidoffice trunks each have a springjack or socketter minal at theirterminal board ends, and a connecting plug adapted for insertion in theline jacks at their connecting board ends; 7u and k2 represent suchspringjacks, while the plugs are shown as being inserted in appropriatesockets K and L7'2 respectively to form a through connection.

At the several terminal switchboard sections d, are provided in theusual way link connections, each composed of flexible conductors withplug terminals; which when thrust respectively into springjacks, effecta thorough connection between the conductors represented by the saidjacks, at the same time severing any original circuit formed Such linkconnections are shown at c at sections d and d2 of terminal switchboardD, and at e2 at Vsection d2 of'terminal switchboard D2.

It will be observed that in the drawings, the link e is shown as unitingthe jack .I of line L to the jack k which is the voffice trunk terminal;the said jacks are shown as being not located on the same but onadjacent terminal sections, a fact which however has no significance.The link c forms the initial union of a through connection, and it isusually desirable that the switchboard section initiating such aconnection, shall also initiate the disconnection when due. For thiscause a clearing out or disconnecting signal as is associated with thelink e. y

The link connection e2 at station O2 is shown as uniting an office trunkjack k2 to asecond jack K2, which as will hereinafter appear, forms oneend of a trunk line extending between the two central stations; sinceconnections as well as disconnections made thereby are uniformly inpursuance of orders made over said trunk line from the distant station,no disconnecting signal for the link connection e2 is required orprovided.

T is an inter-station trunk line extending between the two centralstations O and O2. It unites a springjack K on the connecting board atone of the said stations O with a springjack K2 on the terminal board atthe other station O2. Where such trunk service exists, it usually isconvenient to place their connection beginning ends at the connectingIIO IZO

board, to be reached in the same way as any other called for linethrough an office trunk; and to provide a special section for incomingtrunks, as at d2 on the terminal board, so that trunk calls for otherstations may be received in the same manner as other calls at theterminal board, and may reach a connection with the wanted line at theconnecting board through office trunks also in the same way.

The main line springjacks at the two switchboards as well as the officetrunk connections are associated each with some suitable visual signalindicator, which may be operated by the making of connection ordisconnection at the associated jack or trunk connecting appliance asfully described in my said separate application for patent. To beadapted for this purpose, itis necessary to provide an indicator whichwill become set at any point of a circuit, when a change of condition ismade at a second point; which will stay set until a reversal of suchchange is made; and

which will then respond to such reversal5` thus furnishing a signaldenoting the making, continuance and the dissolution, of theengagementof any circuit conductor where such signal is desired. Such avisual indicator may be formed of the self restoring portion of theannunciator described in Letters Patent of the United States No. 481,120granted to Frank A. Pickernell August 16, 1892, and shown in Fig. 3 ofthis specification. Fig. 4 shows the conventional incandescent or glowlamp, which also is well adapted for the purpose in hand, requiring ofcourse to be properly proportioned to each individual case. I am nothowever restricted to the use of these devices since many other wellknown forms of needle and shutter annunciators will answer equally well.

In the drawings V, V2, V2,V4 and V5 represent the main circuit signalindicators, and n u2 the office trunk signal indicators.

In the present invention, both termini of the inter-station trunkconductors T are also provided with suitable automatically operatedvisual signal indicators e3 and et these each being arranged likewise tobe responsive to connections and disconnections made at the otherterminus, and to be connected and operated in a manner presently to bedescribed.

In Fig. l, the two substation circuitsL and L2, the oflice trunkst andt2, the link connections e and e2 and the inter-station trunk T are allshown as being connected up to form a compound or through circuitextending between the substations A and B through the central stations Oand O2.

Referring now more specially to Fig. 2, L2 is a metallic circuit, 17 and18 being the direct and return conductors thereof, both of which haveseparable contacts in the springjacks g2 and J2. In a central stationwhere both metallic and earth completed substation circuits center, thecircuits of the latter class loop through the switchboards, so that intheir springjacks they may oifer two conductors for connection with thetwo of the metallic circuits. L is such a looped earth completedsubstation circuit, and 1 and 2 are its conductors which pass throughthe spring jacks j and J, and to earth at G. This double conductorconstruction makes it necessary of course, that the office andinterstation trunk circuits t, t2 and T shall in like manner be formedwith double conductors, and accordingly the office trunk t hasconductors 5 and 6; t2 has two conductors 15 and 16, and the twoconductors of the inter-station trunk circuit are marked respectively 9and 10. The same form of springjack may be used for all of the circuitsand conductors and any form of four contact jack will answer. Such aform is indicated at c, K and K2, where m, n, o, p, do, y respectivelyare the main contact springs which only are necessary so far as the mainconductors are concerned. The plug connectors employed must of course beof like but converse construction to the jacks, and comprise fourinsulated conducting surfaces, two of which vn2 and m2 taking the plugP2 for an example, register and make contact with the jack springcontacts m and n.

Of the two plugs of the link connection e, one in Fig. 2 is supposed tobe inserted in the jack J, while the other P2 is ready for insertion inthe jack 7c. The plug P3 of the office trunk t is ready to be insertedin the jack K of the interstation trunk line T. One of the plugs P* ofthe link c2 is ready to be inserted in the other jack K2 of said trunk,while its mate is in the jack 7a2 of the second office trunk; and nallythe plug end of the said oflice trunk t2 is inserted in the jack i2 ofsubstation circuit L2. When all of the plugs are so inserted, thecompound conversation circuit is completed and when both substationcircuits are metallic, is a double conductor circuit throughout: whilewhen one of the substation circuits, is earth completed, the saidcompound circuit is still practically of the double conductor type,since its trunk line is composed of two wires and since one at least ofits ends is looped.

For the purposes of initially signaling either central station from theother, over the main trunk T; of indicating at either end thereof theoccupied condition of said trunk line at the other; and for the promptand automatic announcement at either terminal station of connections anddisconnections made at the other, I associate with the said trunk asystem of reciprocal visual signs whereby the simple act of making aconnection with the trunk line by inserting a plug in its springjack, orof making a disconnection therewith by withdrawing a plug from itsspringjack at either end, is enabled to operate a visual indicator ofthe class to which I have hereinbefore referred, such an indicator beingresponsive both to said connections and disconnections and remaining setas long as the use of the line continues. When both ends of such ICO asystem are located in the same station, it is sulhciently economical toprovide special con-l ductors for the said system; but when the trunkline extends between two stations, it is desirable on account ofconsiderations both of economy and simplicity, to dispense with allconductors which are not absolutely essential; and in view of suchconsiderations I have devised means for operating the necessaryautomatic visual signals reciprocally using no other main conductorsthan the di rect and return conductors 9 and 10 of-the conversationcircuit trunk line itself, these constituting respectively and severallythe main conductors also of the two independent signaling circuitsrequired. this, condensers M, M2, M2, and M4 are interposed between eachend of both conductors 9 and 10 and their respective springjackcontacts. I have found condensers with a capacity of three microfaradsor thereabout to answer perfectly. practical continuity of the circuitwith respect to conversation currents, while they render it impassablefor steady currents such as are used in operating the visual signals.

The trunk line springjack K at O, hasltwo local contact springs fr' ands, for signaling circuits; and the spring jack K2 at O2 also has twolocal signaling circuit spring contacts h and u. These last may ifdesired be electrically united. A branch conductor 23 is led to an earthconnection at station O from any pointf on the main trunk conductor l0outside of the condenser, and in its circuit is included the visualsignal indicator v4 and an electro-magnetic or inductive resistance R2.At the same station a second branch 24 is eX- tended from the point f2on the main trunk conductor 9 to the local sprin gj ack contactrof thejack K. At station O2, the main conductor 9 which is thus left normallyopen in the jack K at O, is provided withan earth branch 25 joining itat the point f2, and included in the circuit of said branch is thevisual signal indicator n3 and the electro-magnetic resistance R2; whilethe main conductor lO which has a closed circuit branch to earth atstation O, is at O2 provided with a branched conductor 31 connectingdirectly to the normally insulated contact springs h andi/,of the jackK2. At station O, the office trunk plug I?3 has a conducting contactsurface w adapted when inserted in jack K to register and make contact`with the spring contact fr. This surface is united to an extraconductor 2O leading to an earth connection through the visual signalindicator o, the electro magnetic resistance R, andan electricalgenerator E which conveniently may be a primary or secondary battery.And in like manner at station O2 the plug P4 has conducting surfacecontacts w3 and 104 adapted when the said plug is inserted in the jackK2 to register and make contact With the spring contacts h and u. Thesesurfaces are both united to a branch conductor 29 leading through theinductive resistance R4 and bat- To accomplish These form no bar to thetery E2 to earth. Thus the two conductors 9 and l0 of the conversationcircuit trunk line, each have a closed earth branch including a signalreceiving instrument at one end, and a Anormally open earth branch atthe other, the

open branch of each being located at the station Where is located theclosed branch of the other. Each also has an inductive resistance ineach earth branch; and a battery in one of them; and each also has asuitable circuit closer in the open branch, operating to close suchbranch by the insertion of the conversation circuit connecting plug, tomaintain the battery current tiowing therein, and through the indicatorat the other station, as long as said plug remains inserted; and to opensuch branch and thereby the circuit of said battery by the withdrawal ofthe said plug. The battery of course may be placed at any point in thebranch at either end.

The inductive resistance is made in a manner Well understood, by windinginsulated copper wire over a properly shaped iron core or cores, theiron preferably having a closed magnetic circuit, and may be wound to areal resistance of about fifty ohms, which alone it practically offersto a steady current such as that employed in the signaling circuit; butadapted in virtue of the arrangement and construction of its winding andiron core to offer an apparent resistance of thirty thousand ohms orthereabout to electrical changes occurring with a velocity of sixhundred per second. These appliances are Well known in the art, and arevariously termed electro magnetic or inductive resistances, andretardation, choking or self-induction coils. Their presence preventsthe diversion of the conversation currents through the earth bran ches,

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while permitting the free passage of the steady signaling current; andon the other hand the condensers prevent the passage of the signalingcurrents, but present no obstacleto the transmission of speech. It willtherefore be seen that a connection made with the double conductor trunkline at station O to form a through telephone circuit, automaticallycloses the circuit of the battery E through one of the conductors 9 ofsuch circuit and the visual signal o2 at station O2, which thereupon isset; that the Withdrawal of the said plug opens the said circuit, andthereupon effects the disappearance of such signal; and that inconsequence of these operations, no connection or disconnection can bemade at O with said trunk without notifying station O2 of such action.And in the same way a connection made at O2 with the said trunk linecloses the circuit of the batteryE2 through the visual signal o4 andgives thereby one signal indicating that the connection called for ismade, while'a disconnection produces a reversal signal and indicatesthat such trunk line is free at O2.

I have not shown or described any call key or telephone loopkey systemin association with the link connections e and e2 at the sta- IIO tionsO and O2, as no such apparatus is required for a clear understanding ot`my invention, but it will of course be understood that any of the wellknown systems of apparatus in which a cam key is supplied with eachlink, controlling the terminals of a telephone and a generator loopmaybe employed.

Although I have described the reciprocal signaling feature of myinvention as being associated with my system of divided switchboards, Idesire it to be understood that it is by no means restricted to suchassociation, but is adapted for use in connection with double conductortrunk lines in any system of switching apparatus.

Having thus fully described and specified my invention I claimz- 1. Thecombination substantially as hereinbefore described, of two dividedswitchboards located at different central telephone stations, and eachcomprising a terminal switchboard at which calls are answered, and aconnectingr switchboard at which connections called for are made; aseries of substation lines centering at each of the said centralstations, each passing through a connection device ou the connectingboard to a second connection deviceon the terminal board; an ofce trunkline at each central station eX- tending from a plugsocket at theterminal board to a connecting plug at the connecting board; and aseries of link connections at each terminal board, each comprising aFlexible conductor and a connecting plug at both ends; with aninter-station trunk line uniting 'the connecting board at one stationwith the tween each terminal section and the main line to constitute thesaid inductive connection thereof.

2. The combination of two divided switchboards located at differentcentral telephone stations, each comprising a terminal switchboard atwhich calls are answered, and aconnectin g switchboard at whichconnections called for are made; aseries of substation circuitsconverging to each of the said central stations, each passing through aplug socket on the connection board to a second plugsocket on theterminal board; an office trunk circuit at each central station joininga plugsocket at the terminal board to a plug connector at the connectingboard; and link connections at each terminal board, each formed of aliexible conductor fitted at both ends with a connecting plug wherebythe plugsockets of the substation and trunk circuits may be united; withan inter-station trunk line uniting a plugsocket on the connecting boardat one central station, to a plugsocket on the terminal board at theother station, the said trunk line comprising a main line section, two

inductively connected terminal sections therefor connected with the saidplugsockets respectively, and a condenser interposed at the junctionbetween each terminal section and the mainline section; and a system ofautomatic signals associated with said interoiiice trunk line andconsisting of a branch circuit at each end, permanently connected to themain line section thereof; one of the said branch circuits being closedthrough asignal indicator and a retardation coil, and the otherincluding a battery, a retardation coil and a circuit closer beingnormally open but adapted to be closed by any connection made with itsassociated plugsocket of said trunk, substantially as hereinbeforedescribed.

3. The combination of two divided switchboards located at differentcentral telephone stations, each comprising a terminal switchboard atwhich calls are answered, andaconnecting switchboard where connectionscalled for are made; a series of substation circuits centering at eachof the said central stations, each passing through a connection deviceon the connecting board to a similar device on the terminal board; anottice trunk line at each central station iitted at the terminal boardwith a plugsocket, and at the connecting board with a plug connector;and link connections at each terminal board, each formed of a flexibleconductor fitted at both ends with a connecting plug adapted forinsertion in the line and ofice trunk sockets; with a double conductoror metallic circuit interstation trunk line uniting a plugsocket on theconnecting board at one central station to a plugsocket on the terminalboard at the other central station, the said trunk line comprising adouble conductor main line section, two inductively connected terminalsections therefor looping to the said plug sockets respectively, andcondensers interposed at the junctions between the two ends of eachterminal loop section and the corresponding ends of the two conductorsot' the main line section; and a reciprocal system ot automatic signalsfor said trunk line comprising a branch circuit at each end of bothconductors thereof, permanently connected with its main line sections,one branch of each of the said trunk conductors at opposite terminalstations being closed through a signal indicator and a retardation coil,and the other including a battery, a retardation coil and a circuitcloser being normally open in the plugsocket of said trunk line, andadapted to be closed bythe insertion of a plug therein, wherebyconnections and disconneotions of said trunk line at either end thereofmay be automatically signaled to the other end substantially asspecified herein.

4. A double conductor trunk line extending between two telephonestations, the two conductors thereof constituting respectively thedirect and return conductors of a conversation circuit, and eachseverally forming a portion ot' an independent signaling circuit.

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5. A double conductor telephone or conversation circuit, and twoindependent signaling circuits extending between two telephone stations;the two conductors of the said telephone .circuit constitutingrespectively the main conductors of the said two signaling circuits,substantially as described.

6. In combination with a double conductor interoflice trunk telephonecircuit adapted to unite the telephone circuits centering in one oflice,with those centering in the other; Va reciprocal signaling Systemcomprising two independent'signaling circuits for indicating at each endof said trunk a connection or disconnection made at the other, the twoconductors of said telephone circuit forming respectively the mainconductors of the two circuits of said signaling system substantially asdescribed.

7. A double conductor trunk line extending between two distant telephonestations, constituting a main line section common" to independenttelephone and signaling circuits, the terminals of the remaining portionof said telephone circuit being inductively connected therewith throughcondensers, and the terminals of the remaining portionof the saidsignaling circuits being conductively connected with the two mainconductors respectively, through electromagnetic resistances, orretardation coils,substantially as described.

8. An interoffice trunk line; a telephone branch or loop therefor atboth terminal ofices; and a condenser interposed at each terminusbetween'the said trunk line and loop;

i combined with anormally closed signal branch including a signalreceiving appliance, and an electromagnetic or inductive resistance,connected with said trunk at one of the said ter- 'mitting branchtherefor, a source of electricminal oflices; a normally open signaltransity, and means as indicated for automatically closing the saidtransmitting branch and for including the-said source therein at theother of said terminal offices substantially as described.

9. The combination with a double conductor trunk telephone lineextending between two stations to form a part of a metallic telephonecircuit, and a condenser in the circuit of each conductor at bothstations; of an earth terminal branch connected with each end of each ofthe said conductors, thetwo earth branches Vboth. earth branches of eachconductor whereby the two conductors of said trunk line are enabledseverally to form portions of inde- Vpermanently connected with each atopposite terminal stations, and including a visual signal indicator; andan Yelectromagnetic resistance or retardation coil; anda normally open YbranchY for the other end of each, at the said opposite stations,including a battery or like generator, a similar electromagnetic resist-Y ance, and a circuit closer adapted to be operated, and to close andopen the signaling circuit by connections or disconnections made :withthe telephone loop at the same station.

ll. The combination of a metallic circuit or double conductor trunk lineuniting two central telephone stations and composed of a doubleconductor main line section, two inductively connected terminal loopsections therefor, one at each station, a springjack in each of the saidloop sections, and condensers interposed between the several ends ofsaid loops and the corresponding ends of the main sections to constitutethe said inductive c'onnection; with two independent earth completedsignaling'circuits associated with said double conductor trunk to.indicate at either end thereof a connection or disconnection madetherewith at the otherend; Vone ofthe said two signaling circuits beingnormally closed, and the other normally open at each of the two terminalstations, and each being composed of a separate one of the trunk mainline sections, a closed and an open branch permanently connected withsaid section, an electromagnetic resistance in each of the said branchesa visual signaling indicator responding to the closing and opening ofthe circuit in the closed branch, a circuit closer in the open branchmounted in the trunk springjack, andV an electrical generator, wherebythe insertion or withdrawal of a plug in or from the springjack ateither end of the trunk line is enabled to operate the signal at theother without necessitating special signaling conductors, substantiallyas described.

In testimony whereof YI have signed my name to this specification, intheY presence of two subscribing witnesses, this 20th day of September,1892.

` EDWARD J. HALL. 1Witnesses:

THos. D. LooKwooD, JOHN C. FREY.

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